The present invention relates to Heating Ventilation and Air Conditioning (HVAC) systems, improving operation of these systems, and providing for improvements in the methods, and/or algorithms used in the management of energy used by these HVAC systems. The present invention relates to the art of providing improved communication and increasing the range and number of thermostats or other comments of a Heating Ventilation and Air Conditioning (HVAC) system connected in a plurality of wireless mesh networks.
Control and communication to and between a number of thermostats and other HVAC components can be provided with a wireless network in which thermostats and other HVAC components serve as nodes in a wireless mesh network. Each of the nodes communicates with other nodes and nodes can forward data from node to node in order to build a network with extended range.
Wikipedia (http://en.wikipedia.org/wiki/Wireless_mesh_network) describes a wireless mesh network as follows.                A wireless mesh network (WMN) is a communications network made up of radio nodes organized in a mesh topology. Wireless mesh networks often consist of mesh clients, mesh routers and gateways. The mesh clients are often laptops, cell phones and other wireless devices while the mesh routers forward traffic to and from the gateways which may but need not connect to the Internet. The coverage area of the radio nodes working as a single network is sometimes called a mesh cloud. Access to this mesh cloud is dependent on the radio nodes working in harmony with each other to create a radio network. A mesh network is reliable and offers redundancy. When one node can no longer operate, the rest of the nodes can still communicate with each other, directly or through one or more intermediate nodes . . . . A wireless mesh network can be seen as a special type of wireless ad-hoc network. A wireless mesh network often has a more planned configuration, and may be deployed to provide dynamic and cost effective connectivity over a certain geographic area. An ad-hoc network, on the other hand, is formed ad hoc when wireless devices come within communication range of each other. The mesh routers may be mobile, and be moved according to specific demands arising in the network. Often the mesh routers are not limited in terms of resources compared to other nodes in the network and thus can be exploited to perform more resource intensive functions. In this way, the wireless mesh network differs from an ad-hoc network, since these nodes are often constrained by resources.        
Energy saving thermostats connected in a wireless mesh network provide for communication between a number of thermostats and one or more central system controllers. There are limits on the size of a single wireless mesh network which are dependent on factors such as the number of messages being sent, the size of the messages or maximum size of the messages, the time and the frequency between nodes receiving and forward messages, the number of wireless frequencies or channels used and other such factors. A limit on the number of nodes in a single wireless network may also be a design choice by the designer of a specific wireless mesh network, and the devices which implement it. For example, a wireless mesh network might be limited to 1024 nodes. A government or regulatory agency may also limit the choice of frequencies, the power, and the number of channels utilized in a network.
In a network of thermostats it is desirable that the thermostats check the status of controlled components fairly frequently such as every fifteen seconds. It may also be desirable for a thermostat to periodically communicate with a central server to receive commands or to report status. A reasonable period for this type of communication would also be every fifteen seconds. For example, it might be desired for an HVAC system controller to receive reports of temperature from every thermostat in the system every fifteen seconds.
It is noted that no matter what frequencies or number of channels are used, or what protocols are utilized with wireless mesh technology there will always eventually be a limit on the number of nodes in a single mesh network if a periodicity of communication between all nodes of the network is a design requirement.